Is support needed when storing for an extended time?

No, but highly recommended.

Until a big wind or other force pushes on the TC you will be fine.

I made mine with one sheet of treated plywood. I made the X. Cut in half short-ways, so two 4 foot squares.
Cut slits of the same width as the board is thick (so 3/4 inch wide slits for a 3/4 inch thick plywood).
Cut the slits only half way. The slits are from the center of one edge to the middle.
Put the two slighted boards together to make an X, or T (+).

Make another one of these.

Put under TC.

You can add boards across the top if you like the camper to sit on more than just two X's.
I put the X's on bricks to keep it off the wet concrete.

This takes weight off TC, but you can still have the legs holding up some weight to give TC a wider footprint.

Others have used a couple of saw horses. Yet others have used stacks of shipping pallets. Bricks. Anything works that you can render....

Not needed, unless you are needing to stabilize it more for say using it while off the truck.
When we first got a TC I thought it was something that was needed, then realized that it's not. Last camper sat for probably 5 years on jacks only.

I never stored my TC unsupported. Safest way is how the TC is supported when on your truck IMO.

I left my big camper on jack only, when it was about 10 yo and after couple of days weight of water tank start separating the floor from the frame.
Camper had some water damages, who participated in floor separation but since that I was always supporting front of camper floor, what also cut down camper movements when we walk inside.
Simple 4x4 at 48" under front floor edge and 4x6 cut to size to keep the camper at optimal level did the trick.
Later on I was able to find aluminium 4x3 tubing, who was better material for the job, but my goal was to carry it with me as we drop camper on our travels quite often

I used to use composite pallets with cross timbers to spread the load. Now I use inexpensive screw jacks (come in sets of four $40) and 4x4's to spread the load. They may not be required, but they definitely help share the load off of just the four corner jacks.

I bought those screw jacks for my van conversion to prevent the movements. Had then originally on 1969 Airstream so this is well-experienced design. You'd be amazed with load capacity of them.

When mine's not on the truck I store it on cinder blocks.

Mine sat on concrete blocks under the floor. Jacks were down to help keep the TC from a blow over from high winds.
I left my first (1972 9' 6") TC lowered just enough we could step up into it and left the TC on the 4 corner jacks from OCT to warm up time in April. The next summer the jacks were so loose and shaky I had to up size all the jacks mounting bolts so they would tighten.
I didn't leave the next two TC we owned on their jacks.
Living in constant high wind parts of the country where all the trees along the road lean in one direction (to the north) we have to be vigilant on sheds....mobilehomes...tall sided rvs having a blow over if exposed to those high winds.

JIMNLIN wrote:
Mine sat on concrete blocks under the floor. Jacks were down to help keep the TC from a blow over from high winds.
I left my first (1972 9' 6") TC lowered just enough we could step up into it and left the TC on the 4 corner jacks from OCT to warm up time in April. The next summer the jacks were so loose and shaky I had to up size all the jacks mounting bolts so they would tighten.
I didn't leave the next two TC we owned on their jacks.
Living in constant high wind parts of the country where all the trees along the road lean in one direction (to the north) we have to be vigilant on sheds....mobilehomes...tall sided rvs having a blow over if exposed to those high winds.

Pretty big leap to make a connection with a camper that was built the year I was born and a new Cirrus….you crack me up.

I've always supported mine for safety. Good thing too as one day in the storage yard someone back their construction trailer so the ladder on the top punched a whole in the front of the cab-over and knocked it back enough to bend two jacks and rip one of them off the rear corner. If it had not been sitting on the trailer which moved with it, it would have fallen and taken out a nice bass boat and utility trailer with it.

I've used several methods over the years. One was four stacks of 4 cement blocks with cross boards. One was cross boards across a 5x8 utility trailer. One was a set of heavy duty sawhorses I custom made. Each had their own pros and cons but all stored the camper at truck bed height. This was important since I have manual jacks so minimal jacking was wanted.